Intradermal injector

ABSTRACT

An injection device that comprises a chamber configured for containing a substance to be injected and a needle operatively associated with the chamber and having a length sufficient to deliver the substance to an intradermal injection site. A collar surrounds the needle, defining a collar cavity. The collar also has a peripheral forward skin-contacting surface that surrounds and is radially spaced from the needle and injection site by an area that is sufficiently large to allow a patient&#39;s skin to move into the collar cavity to properly position the needle for intradermal delivery of the substance to the injection site to allow spread of the injected substance under the skin while inhibiting or preventing backpressure within the skin from forcing the substance out through the injection site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/US03/03917 filed Feb. 11,2003, which claims priority of U.S. Provisional Application No.60/355,926 filed Feb. 11, 2002, the content of which applications isexpressly incorporated herein by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a injection device. More particularly,the invention relates to an intradermal injector to minimize bubbling orblistering of the skin during injection.

BACKGROUND OF THE PRESENT INVENTION

It has been found that intradermal delivery of certain substances andvaccines is more effective than when it is delivered intramuscularly.While traditional jet injectors are known for injecting a substanceintradermally, they are not capable of properly providing an intradermalinjection.

Jet injectors utilize the stream of the injected substance to overcomethe resistance of the skin to penetration. This high velocity stream ofsubstance then also constitutes the substance to be delivered.Traditional jet injectors require high energy to penetrate the toplayers of the skin which provide most of the resistance. Providingsufficient power for such penetration and then depositing the materialto be injected just under the surface skin layer, such as what isrequired for an intradermal injection is challenging. An injection weakenough to administer the material intradermally may be so weak that notall the substance is delivered as the skin surface is not completelypenetrated by the jet. An injection may be to sufficient to deliver theentire substance but so strong that most of the injected substance isdelivered much deeper than the superficial layers of the skin.

Traditional needle injection methods aimed at delivering a substanceintradermally also suffer from major shortcomings. They require a lot ofskill on the part of the person delivering the injection as carefulplacement of the needle as part of the insertion process is required.Injecting the substance to fast from a traditional device by pushing onsubstance being pushed back out of the injection hole once the needle isremoved. The patient is not comfortable during what seems like a longinjection due to the desire to deliver the injected substance slowly toprevent the substance from coming back out of the injection site. Thusimprovements in intradermal injectors are needed.

SUMMARY OF THE INVENTION

The invention relates to an injector, which is preferably an intradermalinjection device. A preferred embodiment of the injector includes achamber configured for containing a substance to be injected. A needleis operatively associated with the chamber and has a length sufficientto deliver the substance to an intradermal injection site. A collarsurrounds the needle and defines collar cavity. The collar has aperipheral forward skin-contacting surface that surrounds and isradially spaced from the needle and injection site by an area that issufficiently large to allow a patient's skin to move into the collarcavity to properly position the needle for intradermal delivery of thesubstance to the injection site and to allow spread of the injectedsubstance at the injection site so as to inhibit or prevent backpressurecausing the injected substance to flow out of the hole created in theskin by the needle after the injection. An energy source preferably isassociated with the needle to assist in delivering the substance to theinjection site. The preferred energy source is configured to provide aninjection assisting pressure of between about 50 and 300 psi to thesubstance.

In this embodiment, the collar has a circular peripheral surface and aninternal diameter of about 4 mm to 7 mm, and the skin-contacting surfaceof the collar is discontinuous. The skin-contacting surface can definediscontinuity gaps, with the skin-contacting surface and gaps togetherdefining a closed shape. The skin-contacting surface preferably occupiesat least about 50% of the closed shape. Additionally, the closed shapeis preferably rounded, but may alternatively be given other suitableshapes. A preferred shape is circular, and the discontinuity gapspreferably are substantially equally spaced along the shape, morepreferably with at least two substantially equally sized continuousportions separated by the discontinuity gaps. The preferred needle isconfigured so that the distal, delivery end thereof is disposed withinabout 0.5 mm of the forward end of the skin-contacting surface.

The invention also relates to a method of intradermal administration ofa substance. In the preferred method, a substance is delivered to anintradermal injection site through a needle while contacting the skinwith a surface that is spaced from the needle by an area surrounding theneedle and injection site. The area is sufficiently large to allow thesubstance to be intradermally injected without causing back pressure atthe injection site in the patient's skin to force any substantial amountof the injected substance out of the needle hole. The delivery of thesubstance is preferably assisted by applying a pressure to thesubstance, preferably about between 50 and 300 psi. The needle can bemoved from a retracted position to an extended position in which theneedle is exposed for injecting the substance into the patient bydrivingly associating a pressurized gas source therewith, the gas can bevented when the substance is injected, and the needle can be biased witha resiliently deformed resilient member to retract the needle when thegas is vented.

The needle of one injector embodiment has a retracted position, whichcan be within the injector body, and also has an extended position, inwhich the needle is disposed for penetrating a patient and injecting thesubstance. A resilient needle cap covers the sharp needle end and isdisposed and configured such that the cover is resiliently deformed withthe needle in the extended position for biasing the needle from theextended position towards the retracted position.

Preferably, the needle is disposed for piercing the cap when moved fromthe retracted position to the extended position. Additionally, oneembodiment has a gas chamber containing a compressed gas and a plungerbiased by the compressed gas with respect to the substance to bedelivered, for forcing the substance through a delivery conduit, such asa needle, for the injecting of the substance. The plunger and the gaschamber are associated such that once the plunger is moved to apredetermined position to inject a predetermined amount of thesubstance, the compressed gas is released from the gas chamber to allowthe cap or other resilient member used to retract the needle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a preferred embodiment of aninjector constructed according to the present invention;

FIG. 2 is a perspective view thereof;

FIGS. 3 and 4 are distal end and perspective views, respectively, of thedistal end thereof;

FIGS. 5 and 6 are distal end and perspective views, respectively, of analternative embodiment of a distal end of an injector; and

FIG. 7 is a cross-sectional view of the injector of FIG. 1 during thefiring thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment shown in FIG. 1, the outer housing 10 includes apreferably elongated and cylindrical body 12 with proximal and distalends 14, 16. As used with respect to the embodiments in thisapplication, the term “distal” designates the end or direction towardthe front of injector, and the term “proximal” designates the end ordirection toward the rear of the injector. A needle opening 18 isdisposed at the forward or distal end of the housing 10 and isconfigured and dimensioned for receiving an injection needle thatextends from the interior of the housing.

A trigger assembly 24 is preferably disposed at the proximal end 14,although in other embodiments is disposed in other portions of theinjector, including at the distal end. The trigger assembly 24 includesa button 26, which is depressible into the housing 10, preferablyaxially, to fire the injector. The trigger assembly 24 preferablyincludes a safety lock to selectively prevent the injector from firing.In the embodiment shown, safety lock 28 is constructed as part of thebutton 26, and can be rotated axially between locked and unlockedpositions to prevent or allow firing of the injector, respectively.

The button 26 is associated with a firing latch that retains a firingmember in a loaded position. The firing member preferably comprises afiring cylinder 30, which is shown in the loaded position in FIG. 1. Thepreferred firing cylinder 30 is substantially cylindrical, with largeand small diameter sections both in the interior bore 32 and also onexterior thereof, although other embodiments have a single inner andouter diameter or other shapes.

Firing cylinder bore 32 receives piston 34, which is preferably fixed tothe outer housing 10. The piston 34 is received in the cylinder bore 32preferably in leak tight association to retain a sufficient amount andpressure of compressed gas in a gas chamber 36, defined between the bore32 and piston 34, to fire the injector. The compressed gas can beprovided in a compressed state or can be a product of a reaction of agas generator therein, such as one activated upon firing of theinjector. A seal 38, such as an o-ring, is preferably disposed in agroove 40 on the piston to seal the gas in the gas chamber 36. Apreferred gas in carbon dioxide, although other suitable gases can beused. Alternative embodiments employ different energy sources to firethe injector, such as coil springs.

A plunger 42 is disposed ahead of the firing cylinder 30 and operativelyassociated therewith so that the firing cylinder 30 forces the plunger42 in a distal direction when the injector is fired. The plunger 42 isreceived within a medicament cartridge 44, which preferably contains amedicament, but alternatively contains another suitable fluid. As shownin FIG. 1, the plunger 42 is disposed in a large diameter portion 46 ofthe medicament cartridge 44.

A hollow injection needle 48 is open to the interior of the medicamentcartridge 44, and is preferably fixed thereto with a proximal sharp end50 protruding into the interior of the cartridge, and a distal sharp end52 protruding beyond the medicament cartridge 44 in alignment with theneedle opening 18. In the preferred embodiment, the proximal sharp end50 of the needle 48 is disposed distally from shoulder 54, whichseparates the large diameter portion 46 from a narrow diameter portion56 and is configured to stop the motion of the plunger 42 in the distaldirection upon contact therewith.

A stopper 60 is disposed in the medicament cartridge 44, preferably inthe narrow portion 56. The stopper 60 seals a medicament chamber 58,which, in the loaded position shown, is defined between the plunger 42and the stopper 60 within the medicament cartridge 44, in the largediameter portion 58. Also, in the loaded position, the stopper 60separates the medicament chamber 58 from the needle 48.

A needle cap 62 is disposed around the needle 48, preferably between theneedle 48 and the needle opening 18, surrounding the front of the distalsharp end 52. The embodiment shown has the needle cap 62 fitted to aneedle holder extension 64 of the medicament cartridge 44. The needlecap 62 is preferably sufficiently resilient to bias and retract thecartridge 44 and needle 48 in a proximal direction, towards the proximalend 14. An alternative embodiment has a needle cap that is mountedoutside of the outer housing. This alternative embodiment preferably hasa resilient element to bias the cartridge and needle in a proximaldirection.

Referring to FIGS. 1-4, a collar 20 preferably surrounds the needleopening 18 on the outside of the outer housing 10. A collar cavity 22 isdefined within the collar 20, and is preferably substantially coaxialtherewith and with the needle opening 18. The collar 20 has a peripheralskin-contacting surface 66 that surrounds and is radially spaced fromthe needle 48 and needle opening 18. This spacing, as well as the axialdepth of the collar cavity are selected to space the skin-contactingsurface 66 from the injection site by an area that is sufficiently largeto allow a patient's skin to move into the collar cavity 22 to properlyposition the needle for intradermal delivery of the substance to theinjection site, preferably without causing a blister or bubble in orunder the patient's skin, and to allow spread of the injected substanceunder the skin while inhibiting or preventing backpressure within theskin from forcing the substance out through the injection site.

The configuration of the injector collar 20 affects the intradermalplacement of the injected substance or medicament. If the collar 20 andcollar cavity 22 is too small in diameter, the substance can be injectedin the form of a blister or bubble that will stretch the outer layer ofskin like a balloon. When the injector is removed, the substance canimmediately exit the bubble through the needle hole, thus losing some orall of the substance from the injection. The preferred skin-contactingsurface 66 is configured to reduce or eliminate this blistering orbubbling effect.

The preferred collar 20 and skin-contacting surface 66 have a closedshape and are rounded, such as having a circular or generally ovalperimeter that contacts the patient's skin. In the embodiment of FIGS.1-4, this perimeter is circular. For most vaccine injections made on thearms or legs of a person, a diameter of at least about 4 mm is desired.Diameters about between 2 mm and 10 mm are preferred, and generally,diameters of about between 4 mm and 7 mm are most useful, depending uponthe substance to be injected.

In the preferred embodiment, the collar 20 and skin-contacting surface66 are discontinuous and define discontinuity gaps 68 that divide theskin-contacting surface 66. The skin-contacting surface 66 is disposedsurrounding the needle opening 18, preferably occupying angularly atleast about 50%, and more preferably at least about 65% and at mostabout 90%, of a phantom closed, continuous shape surrounding needleopening 18 that is defined by the combination of the skin-contactingsurface 16 and the gaps 68. The preferred collar 20 defines two, three,or more gaps 68, or cutout portions of the collar 20, while leavingsufficient surface area of the skin-contacting surface 66 to properlyposition the injector on the skin of the patient without causingdiscomfort and while providing sufficient contact to stretch the skin toenable correct placement of the injection. When the collar 20 orskin-contacting surface 66 is circular, it is preferred to providesubstantially equal amounts of removed areas or gaps 68 in positionsthat are equally spaced around the periphery of the collar 20. Analternative embodiment has a substantially continuous collar with nogaps. The preferred collar 20 has an outer wall 67 with a roundedcross-section, and a substantially flat and axial inner wall 69, andwhich is preferably disposed at an angle of less than about 20° from theaxis. In other embodiments, all walls can be rounded, all flat, or theinner wall can be rounded and the outer wall flat, depending on theintended use.

In another embodiment, a smaller diameter circular or oval collar can beutilized, with a discontinuous skin-contacting surface. This can beachieved by arranging spaced portions of the surface, or by removingportions of the surface. This lessens the force of the collar on theskin to allow the injection to be properly placed between the dermallayers. One desirable arrangement is an evenly divided circular collarthat has two equal sized halves of about 7 mm outer diameter with aninternal opening of about 4 mm. Another embodiment has an oval collardivided along its major or minor axis, or along both. The embodiment ofFIGS. 5 and 6 has a collar 70 that defines an oval collar cavity 72divided along its minor axis, although the outside of the collar has asubstantially circular shape. Thus, the thickness of collar 70 variesalong its periphery.

The skin-contacting surface is configured to contact the skin, as itsname implies. The gaps are configured to release pressure at specificlocations on the skin, and preferably to remain of contact with the skinwhen the injector is pressed against the skin for the injection. In theembodiment shown, the skin-contacting surface 66 is substantiallyplanar, although other suitable shapes can be used.

With reference to FIGS. 1 and 7, to use the injector, the collar 20 isplaced against a user's skin 78, which enters the collar cavity 22. Thebutton 26 is depressed, which causes the latch to release the firingcylinder 30. The compressed gas in the gas chamber 36 acts against thepiston 34 and firing cylinder 30 to bias and move the firing cylinder 30distally, as shown in FIG. 7. The firing cylinder 30 in turn forces theplunger 42 distally, which biases the fluid in the medicament chamber 58and the medicament cartridge 44, which compresses the needle cap 62against distal wall 74 of the outer housing 10. The needle 48 is thusmoved from the retracted position shown to an extended position throughthe needle opening 18, into the collar cavity 72, and a predetermineddistance into the user's skin 78. As piston 42 travels in the distaldirection, it moves the fluid in the medicament chamber 58 distally,causing the stopper 60 to move distally as well. The stopper 60 is thenpierced by the proximal end 50 of the needle 48, placing the interior ofthe needle 48 and the medicament chamber 58 in fluid communication.Continued distal movement of the plunger 60 injects the fluid throughthe needle 48 into the user's skin.

The firing cylinder 30 and the piston 34 are preferably configured torelease he compresses gas from the gas chamber 36. In the embodimentshown, the length of the firing cylinder 30 and the piston are selectedso that beveled portion 76 at the proximal side of the firing cylinder30 is disposed past the seal at the distal side of the piston 34,releasing the seal and letting the compressed gas escape. When the gasescapes, reducing the pressure within the gas chamber 36, the resilientneedle cap 62, or an alternative spring used, retracts the medicamentcartridge 44 and needle 48 in a proximal direction, back into thehousing 10. This arrangement can also be used for firing and releasinggas pressure from an energy source in a jet injector.

In the extended position, the needle 48 can be disposed towards theproximal or distal sides of the forward end of the skin-contactingsurface 66 or substantially flush therewith, depending on the intendeduse. In one preferred embodiment, the needle 48 is disposed at mostabout 1 mm behind or proximally from the forward end of theskin-contacting surface 66 and more preferably at most about 0.5 mm, andat least about flush therewith and more preferably at least about 0.2 mmproximally therefrom. In another preferred embodiment, the needle 48 isdisposed at most about 1 mm ahead of or distally from the forward end ofthe skin-contacting surface 66 and more preferably at most about 0.5 mm,and at least about flush therewith and more preferably at least about0.2 mm or 0.3 mm distally therefrom. One flush embodiment has the needle48 in the extended position disposed between about 0.2 mm to either sideof the forward end of the skin-contacting surface 66, more preferablywithin 0.1 mm, and most preferably within about 0.05 mm or better. Inone embodiment, the position of the distal end of the 48 with respect tothe skin-contacting surface 66 and the shape and size of the collar 20and skin-contacting surface 66 are selected so that the injection depthinto the patient at the injection site is around 0.2 inches.

The fluid substance to be delivered is preferably a solution, and morepreferably a vaccine in liquid form. As noted above, it has been foundthat the intradermal delivery of a vaccine is more effective than whenit is delivered intramuscularly. Relatively small amounts areadministered, typically on the order of about 50 microliters, althoughthe device can be designed to administer between about 25 and 100microliters.

In the preferred embodiment of the present invention, a jet spray is notnecessary, but may be used in an alternative embodiment. The preferredintradermal injection of the substance is assisted by a low pressure.While this pressure varies depending upon the length of the needleprotruding from the injection device, a range of pressures between about50 and 300 psi is generally sufficient to properly administer thesubstance to the desired position and location. In embodiments intendedto inject the fluid no further than the dermis, high pressures thatinject the substance below the dermis rather than between dermal layers,such as those obtainable by conventional needle free injection devices,should be avoided or else the substance will be placed too deeply, thusdefeating the purpose for the intradermal injection. Preferably, thepressure assisted injection is made at pressures of between 65 and 250psi, more preferably between 75 and 150 psi.

This pressure is easily achieved in a device that includes an energysource, such as a coil spring, gas propellant, or a gas spring such asdescribed above. The collar may even be provided on a syringe with thepressure being provided by the strength of the user's thumb indepressing a plunger by a predetermined distance which corresponds tothe delivery of the desired amount of substance. The collar assures thatthe needle is positioned appropriately so that the substance isdelivered properly to the desired location.

In one embodiment, the injection device includes a housing with a skincontacting collar at a distal end of the injector; a retractableinjection-assisting needle at a distal end of the injector; a fluidchamber having an opening for slidingly receiving at least a portion ofthe needle; a plunger movable in the fluid chamber; a trigger assembly;and a energy source operatively associated with the trigger assembly sothat movement of the trigger assembly activates the energy source tomove the plunger in a first direction to expel a fluid from the fluidchamber. The retractable injection-assisting needle has a needle tiplocated at a distal end of the needle and a discharge channel within theneedle tip terminating in an orifice through which the fluid isexpelled. The needle is located within the housing in a retractedposition prior to activation of the energy source. Movement of theplunger in the first direction upon activation of the energy sourceresults in at least a portion of the needle moving forward into the skincontacting collar to a needle insertion point, and expelling fluidthrough the needle tip and past the needle insertion point to a needleinjection site. The needle insertion point is located at the needle tip,and the needle injection site is distal to the needle tip. Theretraction element returns the needle tip to the retracted positioninside the housing after activation of the energy source.

Other suitable injection devices that can be modified to include acollar with a skin-contacting surface are described in U.S. applicationSer. No. 09/779,603, filed on Feb. 9, 2001, the content of which ishereby incorporated herein by reference thereto.

While illustrative embodiments of the invention are disclosed herein, itwill be appreciated that numerous modifications and other embodimentsmay be devised by those skilled in the art. For example, thediscontinuity gaps in the collar may be other than sheer cutouts fromthe collar. The collar may have protruding portions and adjacentrecessed portions, which are the gaps and which may have a continuoussurface with the protrusions around the perimeter and shape followed bythe collar. Therefore, it will be understood that the appended claimsare intended to cover all such modifications and embodiments that comewithin the spirit and scope of the present invention.

1. An intradermal injection device, comprising: a chamber configured forcontaining a substance to be injected; a needle operatively associatedwith the chamber and having a length sufficient to deliver the substanceto an intradermal injection site; and a collar surrounding the needleand defining a collar cavity, the collar having a peripheral forwardskin-contacting surface that surrounds and is radially spaced from theneedle and injection site by an area that is sufficiently large to allowa patient's skin to move into the collar cavity to properly position theneedle for intradermal delivery of the substance to the injection siteto allow spread of the injected substance under the skin whileinhibiting or preventing backpressure within the skin from forcing thesubstance out through the injection site.
 2. The injection device ofclaim 1, further comprising an energy source associated with the needleto assist in delivering the substance to the injection site.
 3. Theinjection device of claim 2, wherein the energy source is configured toprovide an injection assisting pressure of between about 50 and 300 psito the substance.
 4. The injection device of claim 1, wherein the collarhas a circular peripheral surface and an internal diameter of about 4 mmto 7 mm.
 5. The injection device of claim 1, wherein the skin-contactingsurface of the collar is discontinuous.
 6. The injection device of claim5, wherein the skin-contacting surface defines discontinuity gaps, theskin-contacting surface and gaps together defining a closed shape aboutthe needle, wherein the skin-contacting surface occupies at least about50% of the closed shape.
 7. The injecting device of claim 6, wherein theclosed shape is rounded.
 8. The injection device of claim 7, closedshape is circular.
 9. The injection device of claim 5, wherein thediscontinuity gaps are substantially equally spaced along the shape. 10.The injection device of claim 5, wherein the skin-contacting surface hasat least two substantially equally sized continuous portions separatedby the discontinuity gaps.
 11. The injection device of claim 1, whereinthe needle has a delivery end having a position in which it is disposedwithin about 0.5 mm of the forward skin-contacting surface.
 12. Theinjection device of claim 1, wherein the needle and collar areconfigured for injecting the substance intradermally.
 13. The injectiondevice of claim 1, further comprising: a needle having a sharp deliveryend, the needle being operatively associated with the chamber andconfigured dimensioned for delivering the substance to an intradermalinjection site, the needle having a retracted position and an extendedposition in which the needle is disposed for penetrating a patient andinjecting the substance; and a resilient needle cap covering thedelivery end in the retracted position and disposed and configured suchthat the cover is resiliently deformed with the needle in the extendedposition for biasing the needle from the extended position towards theretracted position; a gas chamber containing a compressed gas; and aplunger biased by the compressed gas with respect to the substance forforcing the substance through the delivery conduit for the injecting ofthe substance, wherein the plunger and the gas chamber are associatedsuch that once the plunger is moved to a predetermined position toinject a predetermined amount of the substance, the compressed gas isreleased from the gas chamber to allow the cap to retract the needle.14. An injection device, comprising: a chamber configured for containinga substance to be injected; a needle operatively associated with thechamber and having a delivery end and a length sufficient to deliver thesubstance to an intradermal injection site; and a collar surrounding theneedle and defining a collar cavity, the collar having peripheralforward skin-contacting surface that surrounds the needle and injectionsite by an area; wherein the needle has a delivery position forinjecting the substance into the patient, and the needle delivery end isdisposed at or behind the skin-contacting surface.
 15. A method ofinjecting a substance intradermally, which comprises delivering asubstance to an intradermal injection site through a needle whilecontacting the skin with a surface that is spaced from the needle by anarea surrounding the needle and injection site, which area issufficiently large to allow the substance to be intradermally injectedto allow spread of the injected substance under the skin whileinhibiting or preventing backpressure within the skin from forcing thesubstance out through the injection.
 16. The method of claim 15, furthercomprising assisting the delivery of the substance to the intradermalinjection site by applying a pressure to the substance.
 17. The methodof claim 16, wherein the pressure is about between 50 and 300 psi. 18.The method of claim 15, wherein the skin-contacting surface comprises acollar that is part of an injection device, wherein the collar has acircular peripheral surface and an internal diameter of about 4 mm to 7mm.
 19. The method of claim 18, wherein the skin is contacted by theskin-contacting surface at contact locations separated by discontinuitygaps, the contact locations and the gaps disposed along a substantiallyclosed shape, and the surface at the contact locations occupying atleast about 50% of the closed shape.
 20. The method of claim 19, whereinthe discontinuity gaps are substantially equally spaced from each other.21. The method of claim 18, wherein the collar has at least twosubstantially equally sized continuous portions.
 22. The method of claim16, wherein the needle has a length which sticks out beyond the collarsurface by a distance of up to 0.5 mm.
 23. The method of claim 16,further comprising: moving the needle from a retracted position to anextended position in which the needle is exposed for injecting thesubstance into the patient by drivingly associating a pressurized gassource therewith; venting the gas when the substance is injected; andbiasing the needle with a resiliently deformed resilient member toretract the needle when the gas is vented.
 24. An injection device,comprising: a chamber configured for containing a substance to beinjected; a needle having a sharp delivery end, the needle beingoperatively associated with the chamber and configured dimensioned fordelivering the substance to an intradermal injection site, the needlehaving a retracted position and an extended position in which the needleis disposed for penetrating a patient and injecting the substance; and aresilient needle cap covering the delivery end in the retracted positionand disposed and configured such that the cover is resiliently deformedwith the needle in the extended position for biasing the needle from theextended position towards the retracted position.
 25. The injectiondevice of claim 24, wherein the needle is disposed for piercing the capwhen moved from the retracted position to the extended position.
 26. Theinjection device of claim 25, further comprising: a gas chambercontaining a compressed gas; and a plunger biased by the compressed gaswith respect to the substance for forcing the substance through thedelivery conduit for the injecting of the substance, wherein the plungerand the gas chamber are associated such that once the plunger is movedto a predetermined position to inject a predetermined amount of thesubstance, the compressed gas is released from the gas chamber to allowthe cap to retract the needle.
 27. The injection device of claim 24,further comprising a collar surrounding the needle and defining a collarcavity, the collar having a peripheral forward skin-contacting surfacethat surrounds and is radially spaced from the needle and injection siteby an area that is sufficiently large to allow a patient's skin to moveinto the collar cavity to properly position the needle for intradermaldelivery of the substance to the injection site to allow spread of theinjected substance under the skin while inhibiting or preventingbackpressure within the skin from forcing the substance out through theinjection site.
 28. An injection device, comprising: a substance chamberconfigured for containing a substance to be injected; a gas chambercontaining a compressed gas; a substance delivery conduit associatedwith the substance chamber for injecting the substance into a patient; aplunger biased by the compressed gas with respect to the substance forforcing the substance through the delivery conduit for the injecting ofthe substance, wherein the plunger and the gas chamber are associatedsuch that once the plunger is moved to a predetermined position toinject a predetermined amount of the substance, the compressed gas isreleased from the gas chamber; and a resilient member disposed andconfigured such that the resilient member is resiliently deformed whenthe needle is in the extended position for biasing the needle from theextended position towards the retracted position when the gas isreleased from the chamber.
 29. The injection device of claim 28, furthercomprising a collar surrounding the delivery conduit and defining acollar cavity, the collar having a peripheral forward skin-contactingsurface that surrounds and is radially spaced from the conduit andinjection site by an area that is sufficiently large to allow apatient's skin to move into the collar cavity to properly position theconduit for intradermal delivery of the substance to the injection siteto allow spread of the injected substance under the skin whileinhibiting or preventing backpressure within the skin from forcing thesubstance out through the injection site.